Thread: Running a used Bosch alternator reverse rotation?

Originally Posted by bee utey

Is your 8hp P&S motor sick? I wonder why it has trouble running an alternator putting out less than 1 1/2 hp of electrical power. Perhaps its time to find a Honda or other suitable donor motor.

No, I don't think it's sick.The alternator is bolted to the engine on my belt driven grass slasher that performs much as it always did.The former 80AH one was fitted to an 18hp B&S through a 2:1 step up ratio and would begin charging at startermotor cranking speed before the engine even fired and wouldn't allow the engine to build up RPM unless I first disconnected the hot wire to the alternator.
Fitting serpentine pulleys would be fiddly from the slashers perspective, and is unnecessary, because further Googling indicates that alternators with brushes either new or bedded into the direction of rotation and the correct fan will charge in either direction.
Bill.

While thats true and all on paper....

sometimes the brushes "push" over in the direction of rotation and wear, then when you try turning them backwards they "lift" then burn as they dont have a decent contact patch.

old bosch alt with removeable brush pack should be fine with new brushes.they are very symetrical if not the holder moves a little.

im certian ive come across bosch reversed fan blades on european cars..

comodore 120 amp needs to be spun at high rpm to get these working.
I think its 8 000-up to a max 16 000 RPM.i often ran a small home made pulley on the p76 to get enough speed to charge the battery with a delta wound alt.

a old BMW 6 has a better bosch alt with lots more diodes.